JP2008025005A - Method for producing fine particle of metallic silver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing fine particles of metallic silver having a nanometric size by using silver oxide as a raw material and reducing it in a liquid phase. <P>SOLUTION: This production method comprises the steps of: preparing a dispersion mixture of silver oxide by adding one or more types of aliphatic acids having a 14C or more long-chain in an amount of 0.02 to 0.05 moles in total of the carboxyl group, and a liquid amine compound of 0.12 to 0.35 moles in total of nitrogen atoms in the amino group each with respect to 1 mole of silver atoms contained in powdery silver oxide (I); and stirring and heating it. Thereby, the fine particles with an average size of 3 to 20 nm formed of silver atoms are produced through a reduction reaction in the liquid phase containing the aliphatic acid and the amine compound. The surface of the fine particle of metallic silver is covered with the amine compound through a coordinate bond due to a lone electron-pair existing on the nitrogen atom of the amino group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing fine metal silver particles having a fine average particle diameter by a reduction reaction in a liquid phase using silver oxide as a raw material. In particular, in various fields such as conductive metal pastes and catalysts, metal silver fine particles having an average particle diameter of nanometers and sizes that can be used as a metal powder raw material are used in a liquid phase using silver (I) oxide as a raw material. The present invention relates to a method for producing by a reduction reaction.

  Metal fine particles have been developed for a wide range of applications in various technical fields such as wiring materials, magnetic materials, sensor materials, catalysts, and the like, utilizing the characteristics of the metal elements constituting them. In recent years, as a result of application development and research of these metal fine particles, it has been found that the particle size has a great influence on the performance of final products using metal fine particles. For example, the use of fine metal particles having a very small particle diameter has been studied for the purpose of enhancing the functionality and size of the final product. In accordance with the purpose, for a large number of kinds of metal elements, fine particles having extremely fine particle diameters, more specifically, metal nanoparticles having an average particle diameter of submicron and even a nanometer scale are prepared. Various methods have been reported.

  In the case of metal fine particles having an average particle diameter of submicron or nanometer scale, the spherical surface of the fine particles is composed of fine step-like lattice steps. Compared with metal atoms present on a planar surface, metal atoms appearing on this fine step-like lattice step are unique to metal nanoparticles, for example, the mobility on the surface is significantly increased. Special properties (nano-size effect). By applying such unique properties to metal nanoparticles, the possibility of enhancing the performance of derived products or adding new functions has been studied, and in recent years, new application development of metal nanoparticles has become increasingly popular. It is becoming. For example, in anticipation of a major technical contribution to the miniaturization of wiring corresponding to miniaturization of electronic equipment, with regard to the formation of fine silver particles with high thermal conductivity and electrical conductivity, and the use of silver fine particles Many considerations have been made.

  As a method for producing fine silver fine particles having an average particle diameter of nanometer scale, a method of producing silver fine particles by a gas evaporation method (gas phase method) is known (see, for example, Patent Document 1). Using this gas evaporation method (gas phase method), the silver vapor pressure of the silver is controlled to prepare the fine silver particles with the desired average particle size of nanometer scale with high controllability and reproducibility. It is possible. However, the production of metal nanoparticles by the vapor phase method requires a special apparatus. When applied to mass production, there is a difficulty in economics from the viewpoint of equipment and energy efficiency. Yes.

Further, the fine particles of silver aliphatic monocarboxylate (C _n H _{2n + 1} COOAg: n = 4 to 17) exceed the melting temperature, but are sufficiently lower than the complete thermal decomposition temperature, for example, about 250 ° C. When heat treatment is performed at a temperature, part of the solution is liquefied, and then thermal decomposition proceeds with decarboxylation from the aliphatic monocarboxylic acid residue (C _n H _{2n + 1} COO—). As a result, for example, it has been reported that silver nanoparticles having a particle size distribution similar to monodispersion having an average particle size of about 5 nm are generated (Non-Patent Document 1). At that time, the long-chain alkyl group (C _n H _{2n + 1} —) derived from the decarboxylation process remains on the surface of the silver nanoparticles to be produced, and the surface functions as a protective group for the surface. It has been reported. The solid phase aliphatic monocarboxylic acid silver is subjected to a heat treatment at a high temperature for thermal decomposition. For example, CH ₃ (CH ₂ ) ₁₂ COOAg, CH ₃ (CH ₂ ) ₁₆ COOAg, CH _{3 (CH 2) 7 CH = CH} (CH 2) 7 COOAg has also been reported to be applicable to (Patent Document 2).

In addition, when a fine powder of silver myristate (CH ₃ (CH ₂ ) ₁₂ COOAg) is heated to 80 ° C. in triethylamine, an amine reduction reaction proceeds on the surface of the fine powder of silver myristate that is insoluble in triethylamine. However, it has been reported that silver nanoparticles having a particle size distribution similar to monodispersion having an average particle size of several nanometers are produced (Non-Patent Document 2).
Japanese Patent No. 2561537 Japanese Patent No. 3205793 K. Abe et al. , Thin Solid Films, Vol. 327, 524-527 (1998) M.M. Yamanoto and M.M. Nakamoto, J. et al. Mater. Chem. , Vol. 13, 2064-2065 (2003)

  When producing uniform metallic silver fine particles having an average particle diameter of nanometers, for example, about several nanometers to several tens of nanometers, a method for producing silver fine particles by a liquid phase method using silver fatty acid monocarboxylate as a starting material is Is a useful tool. When purified fatty acid monocarboxylate silver salt that is a starting material is available at a low cost, for example, silver nanoparticles produced by an amine reduction reaction using triethylamine are converted to the starting fatty acid monocarboxylate silver salt. On the other hand, it is a method that generates almost equal amounts and is suitable for mass synthesis.

  The raw material fatty acid monocarboxylate silver is produced, for example, by a method of depositing insoluble fatty acid monocarboxylate silver from fatty acid monocarboxylate sodium and silver nitrate as the anion species is exchanged. Furthermore, nitrate anion species and the like mixed in the reaction system are removed, and the precipitated insoluble fatty acid monocarboxylate is purified.

  Without preparing insoluble fatty acid monocarboxylate in advance, metallic silver fine particles having a fine average particle diameter are prepared by a reduction reaction in a liquid phase using readily available silver oxide (I) as a starting material. If a method is developed, it becomes a manufacturing method greatly simplified in consideration of the whole process.

  The present invention solves the above-mentioned problems, and the object of the present invention is to produce uniform silver fine particles having an average particle diameter of several nanometers to several tens of nanometers by a liquid phase method using silver oxide as a starting material. It is to provide a method that makes it possible.

  The inventors of the present invention have made extensive studies to solve the above problems. First, when the starting silver oxide (I) is directly reduced, the silver atoms generated on the surface of the finely divided silver oxide (I) are integrated with the original fine powder. As a result, it has been found that it is difficult to produce silver fine particles having a particle size of nanometer size, which is much smaller than the size of the raw fine powder.

Therefore, it is determined that it is necessary to apply a technique in which the silver cation species (Ag ⁺ ) is once eluted from the finely powdered silver oxide surface and then reduced to silver atoms in the liquid phase. did. At that time, if the density of silver atoms generated by the reduction reaction is controlled per unit volume and unit time in the liquid phase, the average particle diameter of the silver fine particles formed by the aggregation of the generated silver atoms is reduced to the nanometer size. The idea was that it could be controlled with good reproducibility within the range of. In other words, the fine powder of silver (I) oxide surface, when eluting the silver cation species (Ag ⁺⁾ once, unit volume, per unit time, the silver cation species eluted into the liquid phase (Ag ⁺ When the density of () is optimized, the density of silver atoms generated by the reduction reaction per unit volume and unit time can be controlled. Therefore, the silver atoms of this limited density gather and the size of the formed metal silver fine particles is controlled within a certain range. In addition, when the surface of the metal silver fine particles to be formed is coated with molecular species that have affinity for silver atoms, when a certain particle diameter is reached, further adhesion of silver atoms is suppressed. It has also been found that the particle diameter of metallic silver fine particles formed in the liquid phase can be controlled within a narrow range.

As a molecular species that has an affinity for silver atoms that can be used to coat the surface of the formed metal silver fine particles, the amine compound is coordinated by using a lone pair of electrons on the amino nitrogen atom. It was thought that it can be performed and it can utilize suitably. On the other hand, in the process of eluting silver cation species (Ag ⁺ ) from the finely powdered silver (I) oxide surface, aliphatic carboxylic acids, particularly aliphatic monocarboxylic acids can be used. Silver cation species (Ag ⁺ ) can be eluted in the liquid phase as acid silver, in particular, aliphatic monocarboxylic acid silver. In the liquid phase, in the presence of an amine compound, this silver aliphatic carboxylate, in particular, the silver cation species (Ag ⁺ ) of silver aliphatic monocarboxylate is reduced to produce silver atoms.

  In consideration of the above examination results, the present inventors have further studied, and the silver atoms to be formed are aggregated, and the formed metal silver fine particles have a particle diameter of about several nanometers to tens of nanometers. It was found to be kept in the range and dispersed and suspended in the liquid phase. That is, an amine compound or the like present in the reaction system is coordinated to the surface silver atoms, and the surface of the metal silver fine particles is coated with a dispersant and dispersed in the solvent. At the same time, it was found that the surface coating layer exerts an inhibitory action on the aggregation of the metallic silver fine particles.

In the series of reaction processes described above, an aliphatic carboxylic acid, particularly an aliphatic monocarboxylic acid, is equivalent (1 mol amount) to 1 mol amount of silver cation species (Ag ⁺ ) in silver (I). Even when the reaction temperature is selected to be high, the aliphatic carboxylic acid produced per unit volume and unit time is added in a much smaller amount, specifically 0.05 mol or less. The amount of silver, especially the silver aliphatic monocarboxylate, can be controlled, while the amine compound is a large excess with respect to the aliphatic carboxylic acid, specifically, the aliphatic carboxylic acid: amine. The ratio of the compound is at least in the range of 1 mol amount: 3 mol amount or more, provided that it is in the range of 0.35 mol amount or less with respect to 1 mol amount of silver cation species (Ag ⁺ ) in silver (I) oxide. By adding to the unit volume, unit volume, unit time Generated Ri, it was confirmed that it is possible to control the amount of silver atoms. In addition to these findings, the present inventors have made the aliphatic carboxylic acid, particularly the aliphatic monocarboxylic acid and the amine compound, uniformly dissolved in the liquid phase in the reaction in the liquid phase. Therefore, it was confirmed that it is generally desirable to carry out the reaction by heating and stirring after avoiding evaporation / dissipation of fatty acids and amine compounds, and the present invention has been completed.

That is, the method for producing metal silver fine particles according to the present invention includes
A method of preparing metal silver fine particles having an average particle diameter of 3 nm to 20 nm by a reduction reaction in a liquid phase using silver oxide as a raw material,
Per mole of silver atoms contained in the powdered silver oxide (I),
One or more fatty acids selected from saturated aliphatic carboxylic acids or unsaturated aliphatic carboxylic acids, in an amount such that the sum of the carboxy groups is 0.02 to 0.05 mol,
A liquid amine compound is added in an amount such that the sum of amino nitrogen atoms is 0.12 to 0.35 mol,
A nonpolar solvent is added, and the silver content in the mixed solution is selected in the range of 25% by mass to 40% by mass,
Preparing a silver oxide dispersion mixture in which the powdered silver oxide (I) is dispersed in a mixture in which the fatty acid and the amine compound are uniformly mixed;
The silver oxide dispersion mixture is heated and stirred at a liquid temperature selected in the range of 80 ° C. to 140 ° C., and the amino compound is in a liquid phase comprising a mixture in which the fatty acid and the amine compound are uniformly mixed. In the presence of water, the fatty acid is allowed to act on the silver oxide (I) to form the corresponding fatty acid silver (I), and thereafter, metal silver fine particles having an average particle diameter of 3 nm to 20 nm consisting of silver atoms generated by reduction are precipitated. And
The metal silver fine particles having an average particle diameter of 3 nm to 20 nm to be deposited are coordinated with respect to silver atoms on the surface using at least the lone electron pair in which the amine compound is present on the amino nitrogen atom. A method for producing metal silver fine particles, characterized in that the metal silver fine particles are coated through various bonds.

  In this case, the fatty acid is preferably selected from linear alkanoic acids having 14 to 22 carbon atoms or linear alkenoic acids having 14 to 22 carbon atoms.

On the other hand, the liquid amine compound has a boiling point of 80 ° C. or higher, a primary amine (R ¹ NH ₂ ), a secondary amine (R ¹ R ² NH), and a tertiary amine (R ¹ R ² R ³ N). One kind of amine selected from the group consisting of or two or more kinds of amines is preferable. Among these, the liquid amine compound includes a primary amine (R ¹ NH ₂ ), a secondary amine (R ¹ R ² NH), and a tertiary amine in which the hydrocarbon group substituted on the amino nitrogen atom is an alkyl group. More preferably, it is one kind of alkylamine selected from the group consisting of (R ¹ R ² R ³ N), or two or more kinds of amines. At least the liquid amine compound is desirably a trialkylamine having a boiling point exceeding 140 ° C.

In the method for producing metallic silver fine particles according to the present invention,
In the heating and stirring of the silver oxide dispersion mixture, the heating temperature of the liquid phase is at least 80 ° C. or more, and the temperature at which the mixture of the fatty acid and the amine compound is uniformly mixed can form a uniform mixed solution. It is desirable that the temperature be selected so that it does not exceed the boiling point of the liquid amine compound itself. For example, in heating and stirring the silver oxide dispersion mixture, the heating temperature of the liquid phase is selected to be at least 100 ° C. or higher and not exceeding the boiling point of the liquid amine compound itself.

  On the other hand, when a nonpolar solvent is added to the reaction solution, the nonpolar solvent is a nonpolar solvent capable of forming a uniform mixed solution with the liquid amine compound at the heating temperature of the liquid phase. preferable. For example, the nonpolar solvent is more preferably selected from toluene, xylene, and a hydrocarbon solvent having a boiling point of 90 ° C. or higher.

  On the other hand, in the reduction reaction step, it is desirable to use an inert gas when venting the reaction system, for example, at least one selected from the group consisting of nitrogen, argon, and helium. . In addition, a reaction system employing a reflux condenser having a function of refluxing the nonpolar solvent for the purpose of avoiding transpiration of the nonpolar solvent added to the reaction liquid at the liquid temperature during the heating is configured. Is desirable.

  The method for producing metal silver fine particles according to the present invention is conventionally produced by a so-called liquid phase method using a previously prepared silver aliphatic monocarboxylate as a raw material and applying an amine reduction method in the presence of a large excess of amine. It is possible to more easily produce silver fine particles having a nano-level fine particle diameter, using silver (I) oxide as a raw material. In addition, the silver fine particles having a nano-level fine particle size are present on the amino nitrogen atoms with at least an appropriate amount of an amine compound added to the reaction system with respect to the silver atoms on the surface. Silver nanoparticles with a coating agent of amines, which can be formed by coating via a coordinated bond using a lone pair of electrons, and produced by gas evaporation (gas phase method) It can also have equivalent dispersion stability. That is, a silver fine particle having a nano-level fine particle diameter obtained by the production method according to the present invention is to apply a method of reducing aliphatic monocarboxylic acid silver with an amine or a gas evaporation method (gas phase method). Compared with fine silver fine particles having an average particle diameter of nanometer scale, which are manufactured in 1), the quality is comparable. Therefore, the manufacturing apparatus cost in the liquid phase method is remarkably low compared with the manufacturing apparatus cost in the gas evaporation method (gas phase method), and in addition, an extra step for preparing the aliphatic monocarboxylate in advance. This is a useful production method for mass-producing silver fine particles having a high quality nano-level fine particle diameter at a lower production cost.

The conventional method for producing silver fine particles having a nano-scale fine particle size by liquid phase method is to prepare and purify insoluble fatty acid silver from silver nitrate and fatty acid sodium in advance, and then add a large excess of amine compound. This was a technique for producing silver nanoparticles having an average particle diameter of several nm by amine reduction of the fatty acid silver (I) in the presence. On the other hand, the method for producing metal silver fine particles according to the present invention utilizes silver (I) oxide as a raw material, and selects an amine when selecting a high reaction temperature with respect to the amount of silver (Ag ⁺ ) contained. In the presence of the compound, an amount (less than 1/20) of a fatty acid much smaller than the equivalent is allowed to act on silver oxide (I) to gradually convert it into fatty acid silver (I), followed by reduction. This makes it possible to produce silver nanoparticles having an average particle diameter of 3 nm to 20 nm, preferably 4 nm to 15 nm, and having an average particle diameter of several nm. At that time, the silver fine particles having a nano-level fine particle diameter formed from silver atoms generated by amine reduction are at least an amine compound added in an excessive amount in the reaction system with respect to the silver atoms on the surface. The lone electron pair present on the amino nitrogen atom is used to form a coating formed through a coordinate bond. Therefore, in the non-polar solvent, the organic molecular layer covering the surface of the silver fine particles prevents the aggregation of the silver fine particles and exhibits a function of maintaining a uniformly dispersed state, resulting in excellent dispersion stability. It becomes.

  Hereinafter, the present invention will be described in more detail.

In the method for producing metal silver fine particles according to the present invention, first, fine powdery silver oxide (I) (Ag ₂ O; molecular weight 231.74), a fatty acid and a liquid amine compound are mixed, and the fatty acid and the liquid amine are mixed. A dispersion is prepared by dispersing finely powdered silver oxide (I) in a mixture containing the compound. At that time, a nonpolar solvent is added to adjust the fatty acid, the concentration of the liquid amine compound, and the dispersion density of the finely powdered silver oxide (I) in the dispersion.

As the nonpolar solvent used as the diluting solvent, at least a nonpolar solvent capable of forming a uniform solution with the liquid amine compound used in excess is used. On the other hand, the fatty acid used is selected from aliphatic carboxylic acids, particularly saturated aliphatic monocarboxylic acids or unsaturated aliphatic monocarboxylic acids, and is usually a liquid amine or a liquid amine used at room temperature. Those that are readily soluble in the compound are used. At least when the liquid temperature is 80 ° C. or higher, the fatty acid that forms a uniform mixed solution with the liquid amine compound is preferably used. In general, aliphatic monocarboxylic acids (R′-COOH) are liquid amine compounds such as primary amines (R ¹ NH ₂ ), secondary amines (R ¹ R ² NH), tertiary amines (R ¹ R ² R ³ N) and, for example, R′—COOH... NR ¹ R ² R ³ can be formed, and the liquid amine compound itself or the liquid amine compound can be easily dissolved. It can be uniformly dissolved in a nonpolar solvent.

The shape of the raw fine powdered silver oxide (I) (Ag ₂ O; molecular weight 231.74) itself is not particularly limited, but for uniform dispersion in the liquid while heating and stirring the reaction liquid, A particle size distribution that falls within a range of 200 mesh or less (75 μm or less) is preferably used. Since the crystal lattice of silver (I) oxide has a body-centered cubic lattice (bc), the crystal lattice of a single metal silver having a cubic close-packed structure, a face-centered cubic lattice (f. c.c.) and X-ray diffraction.

In the present invention, for finely divided silver oxide (I) (Ag ₂ O), in the presence of an amine compound, for finely divided silver oxide (I) (Ag ₂ O), fatty acid (R ′ -COOH) is allowed to act to produce fatty acid silver (R'-COOAg) in the reaction system. Subsequently, the produced fatty acid silver is subjected to amine reduction to produce silver atoms. For example, two silver atoms are produced from silver (I) oxide (Ag ₂ O) through an elementary reaction process that can be promoted by the amine effect as described below. Oxidation to type compound [R ¹ R ² R ³ N ⁺ —O ⁻ or R ¹ R ² R ³ N → O]. At that time, the fatty acid (R′-COOH) itself is used in the initial elementary reaction process, but is regenerated during a series of processes.
(I) Ag ₂ O + R′—COOH → [R′—COOAg + AgOH]
(Ii) R′-COOAg + R ¹ R ² R ³ N → [R′-COOAg... NR ¹ R ² R ³ ]
^{→ [R'-COO - + Ag} + R 1 R 2 R 3 N + ·]
(iii) R′—COO ⁻ + AgOH → [R′—COOH + Ag—O ⁻ ]
(iv) [R ¹ R ² R ³ N ⁺ · + Ag-O ⁻ ] → [R ¹ R ² R ³ N ⁺ —O ⁻ + Ag]
(V) [R ¹ R ² R ³ N ⁺ —O ⁻ ] → [R ¹ R ² R ³ N → O]
On the other hand, the amine oxide type compound [R ¹ R ² R ³ N ⁺ —O ⁻ or R ¹ R ² R ³ N → O] produced in the reaction process described above is a fatty acid (R ″ —CH ₂ —CH ₂ — by oxidizing COOH), again, the amine compound ^{[R 1 R 2 R 3 N} ] is reproduced. by this regeneration process, the amine compound in the reaction system of the ^{[R 1 R 2 R 3 N} ] The concentration is kept within a certain range.
(Vi) 3 [R ¹ R ² R ³ N → O] + R ″ —CH ₂ —CH ₂ —COOH
^{→ [3 · R 1 R 2} R 3 N + CO 2 + R "-CH 2 -C (OH) 3]
^{→ 3 · R 1 R 2 R} 3 N + CO 2 + H 2 O + R "-CH 2 -COOH
That is, the number of carbon atoms is reduced by one due to the steps (vi-1) to (vi-3) in which fatty acids (R ″ —CH ₂ —CH ₂ —COOH) are oxidized stepwise with decarboxylation. Converted to fatty acid (R ″ —CH ₂ —COOH). This fatty acid (R ″ —CH ₂ —COOH) is reused in the above elementary reaction step (i). Therefore, the total sum (concentration total) of fatty acids present in the reaction system is kept within a certain range. Is done.
(Vi-1) [R ″ —CH ₂ —CH ₂ —COOH + O]
→ CO ₂ ↑ + [R "-CH ₂ -CH ₂ -OH]
(Vi-2) [R " -CH 2 -CH 2 -OH + O]
_{→ [R "-CH 2 -CH (} OH) 2]
(Vi-3) [R ″ —CH ₂ —CH (OH) ₂ + O]
_{→ [R "-CH 2 -C (} OH) 3]
→ H ₂ O + R ″ —CH ₂ —COOH
(I′-0) Ag ₂ O + H ₂ O → [2AgOH]
(I′-1) [2AgOH] + R ″ —CH ₂ —COOH
_{→ [R "-CH 2 -COOAg +} AgOH] + H 2 O
Since the above process (vi) is a reaction involving decarboxylation, it does not proceed when the reaction temperature is low. However, in the present invention, at least the reaction temperature is increased to 80 ° C. to increase the reaction rate. Yes. As a result, the amine compound [R ¹ R ² R ³ N] used in the reduction reaction is regenerated, and the overall reaction between the elementary reaction processes (i) to (v) and the process (vi) is performed. Speed equilibrium is achieved.

In the step (vi), water molecules (H ₂ O) by-produced are converted into solid phase silver oxide (I): Ag ₂ O through the above-mentioned secondary step (i′-0). Is utilized in the process of converting to the form of silver hydroxide: AgOH. As a result, it is estimated that no water molecules (H ₂ O) are accumulated in the liquid phase of the reaction system. On the other hand, in the subsequent reaction of the elementary process (vi-3), the equilibrium constant K (vi-3) of the reaction is K (vi-3) = {[H ₂ O] · [R ″ -CH ₂ —COOH. ]} / [R ″ —CH ₂ —C (OH) ₃ ], but it is avoided that the progress of this reaction is inhibited by the accumulation of free water molecules (H ₂ O).

  Therefore, in the present invention, the amount of fatty acid blended in the reaction solution per mole of silver atoms contained in the powdered silver oxide (I) is much less than the equivalent, 0.05 mole amount. It is possible to select a range below. Specifically, an aliphatic carboxylic acid, in particular, a fatty acid selected from a saturated aliphatic monocarboxylic acid or an unsaturated aliphatic monocarboxylic acid per mole of silver atoms contained in powdered silver oxide (I) One or more, in an amount such that the sum of the carboxy groups is 0.02 to 0.05 mol, preferably in the range of 0.025 to 0.045 mol, usually 0.03 to 0.04 mol Can be used.

In the above series of reactions: (i) to (vi), when reducing three molecules of silver oxide (I) (Ag ₂ O), aliphatic carboxylic acid (R ″ —CH ₂ —CH ₂ —COOH) , One carbon is lost and converted to an aliphatic carboxylic acid (R ″ —CH ₂ —COOH). When reducing the amount of 1 mol of silver atoms contained in the powdered silver oxide (I), 1/6 mol of the aliphatic carboxylic acid consumes one carbon. For example, when 0.02 mole amount of a linear alkanoic acid having 14 carbon atoms is used and 10 carbon atoms are consumed until a linear alkanoic acid having 4 carbon atoms is obtained, the target silver oxide (I) (Ag With respect to ₂ O), 0.02 × 3 × 10 = 0.6 molar amount is reduced. In other words, the reduction treatment is performed by using, for example, 0.02 mol of linear alkanoic acid having 14 carbon atoms per 1 mol of silver atoms contained in the powdered silver oxide (I). Is possible.

  As the fatty acid to be used, a saturated aliphatic monocarboxylic acid or an unsaturated aliphatic monocarboxylic acid, preferably a linear alkanoic acid having 14 to 22 carbon atoms or a linear alkenoic acid having 14 to 22 carbon atoms is selected. In particular, it is more preferable to select a linear alkanoic acid having 14 to 18 carbon atoms or a linear alkenoic acid having 14 to 18 carbon atoms. In general, in an aliphatic monocarboxylic acid, the number of carbon atoms decreases and acid dissociation easily occurs. In other words, the reaction rate of the elementary process (i) increases. As a result, when the amount of silver atoms generated per unit time and unit volume increases, the average particle diameter of the formed metal silver fine particles also increases. In order to keep the average particle diameter of the target metallic silver fine particles of several nm, for example, a suitable range of 3 to 20 nm, and more preferably 4 to 15 nm, the reaction rate of the elementary process (i) is controlled. There is a need. Specifically, it is necessary not to unnecessarily increase the reaction rate of the elementary process (i), and the number of carbon atoms of the aliphatic carboxylic acid to be used, particularly the aliphatic monocarboxylic acid, should be selected within a certain range. Is preferred.

Further, the amine oxide type compound [R ¹ R ² R ³ N ⁺ —O ⁻ or R ¹ R ² R ³ N → O] produced as a by-product is converted into the amine compound [R ¹ R ² R via the step (vi). ³ N] for playing, in the present invention, silver atoms 1 molar amount per contained powdered silver oxide (I), the amount of amine compound mixed in the reaction solution, much less than the equivalent amount , It is possible to select a range below 0.35 mol. Specifically, the amine compound is added in an amount such that the total amount of amino nitrogen atoms is 0.12 to 0.35 mol per mol of silver atoms contained in the powdered silver oxide (I), preferably 0. A range of .15 to 0.30 moles, more preferably 0.2 to 0.3 moles, can be used.

At that time, the amine compound [R ¹ R ² R ³ N] per molecule of fatty acid (R ″ —CH ₂ —CH ₂ —COOH) used is at least 3 molecules, preferably 4 molecules or more. An existing state can be achieved.

  In practice, it is necessary to set the reaction liquid temperature to a certain level in order to keep the overall reaction time within a reasonable range. At this time, the reaction rate of the elementary process (i) is accelerated at an accelerated speed as the reaction solution temperature increases. Therefore, if the reaction liquid temperature is increased and at the same time, an aliphatic carboxylic acid to be used, for example, an aliphatic monocarboxylic acid having high reactivity is used, the reaction rate of the elementary process (i) becomes unnecessarily large. As a result, the average particle diameter of the formed metallic silver fine particles is less than the target range of less than 100 nm, for example, greatly exceeds the preferred range of 3 to 20 nm. As the aliphatic carboxylic acid to be used, in particular, as an aliphatic monocarboxylic acid, a straight chain alkanoic acid having 14 to 22 carbon atoms or a straight chain alkenoic acid having 14 to 22 carbon atoms, more preferably a straight chain having 14 to 18 carbon atoms. When the chain alkanoic acid or the straight chain alkenoic acid having 14 to 18 carbon atoms is selected, the concentration is lowered. Therefore, the reaction of the elementary process (i) is performed even under the condition that the reaction liquid temperature is increased to about 140 ° C. It becomes easier to keep the speed within the target control range. In linear alkanoic acid and linear alkenoic acid, the melting point increases as the number of carbon atoms increases. Therefore, when forming a uniform liquid phase with the amine compound to be used in the reaction solution, the solvent is nonpolar. It is essential to use a solvent. In addition, in linear alkanoic acid and linear alkenoic acid, the reactivity increases as the number of carbon atoms increases, but sufficient reaction can be achieved even under conditions where the amount of fatty acid used is suppressed by increasing the reaction temperature. Speed can be achieved.

  At that time, if a straight chain alkanoic acid having 14 to 18 carbon atoms or a straight chain alkenoic acid having 14 to 18 carbon atoms is selected, it becomes liquid when the liquid temperature reaches about 60 ° C., so it is uniform in a nonpolar solvent. It will be in a dissolved state. That is, a liquid phase in which the amine compound and the fatty acid are uniformly dissolved in the nonpolar solvent can be obtained. On the other hand, under conditions where the reaction temperature is considerably high, the reactivity is within an appropriate range as a whole even if the concentration is low. When at least the reaction temperature is 80 ° C. or higher and 100 ° C. or lower, it is a more preferable selection range for fatty acids.

In addition, in the above-mentioned elementary process (i), the long-chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH) corresponds to the corresponding long-chain monocarboxylic acid on the surface of silver oxide (I). Like (CH ₃ — (CH ₂ ) _m —COOH), only the carboxy group (—COOH) at one end of the long-chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH) can act. Therefore, a long-chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH) can be used instead of the corresponding long-chain monocarboxylic acid (CH ₃ — (CH ₂ ) _m —COOH). At that time, for the long-chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH), instead of the total of the two carboxy groups (—COOH) contained, one carboxy group (—COOH) involved in the reaction is used. ).

Specifically, the long-chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH) is obtained by the above elementary process (vi-1):
(Vi-1) [HOOC- ( CH 2) m -COOH + O]
→ CO ₂ ↑ + [HO- (CH ₂ ) _m-1 -COOH]
To ω-hydroxyalkanoic acid (HO— (CH ₂ ) _m−1 —COOH). Therefore, since it contributes as long-chain ω-hydroxyalkanoic acid (HO— (CH ₂ ) _m−1 —COOH) in the above elementary process (i), the carboxy group (—COOH) When performing the summation, it is treated as a substantially monocarboxylic acid.

On the other hand, a fatty acid having a branch, in particular, a branched chain exists on the carbon atom at the α-position of the carboxylic acid: a fatty acid in the form of R ⁴ —CH (R ⁵ ) —COOH is a fatty acid having no corresponding branched chain: R ⁴ differs from the -CH ₂ -COOH, the reaction process described above (vi) does not proceed. Considering this point, when using a branched fatty acid, it is possible to select one having at least a linear alkylene chain having 10 or more carbon atoms (— (CH ₂ ) _m —) from the carboxy group side. preferable.

  On the other hand, the reaction solution temperature is desirably set in a range not exceeding the boiling point of the amine compound used in the reduction reaction involving the amine compound, such as elementary processes (ii) to (iv). Since the reaction itself is carried out under reflux, the amine compound is prevented from evaporating and dissipating, but when the proportion of the amine compound present as vapor in the gas phase in the reaction vessel becomes higher than necessary, The amine compound concentration in the reaction solution is relatively reduced. Also, the amine compound used for coating the surface of the metal silver fine particles once formed becomes prominent, and as a result, the generated silver atoms are further accumulated in the formed metal silver fine particles. The average particle diameter of the obtained metal silver fine particles greatly exceeds the target range of 3 to 20 nm, for example, the range of 4 to 15 nm. Considering this point, the reaction solution temperature is generally set in a range not exceeding the boiling point of the amine compound to be used.

  In the silver oxide dispersion mixture, if the fatty acid and the amine compound are dissolved at a high concentration, the fatty acid can act on the surface of the silver (I) oxide even at room temperature, and the above elementary process (i) proceeds. . At that time, if the amine compound is dissolved at a high concentration, the reduction reaction involving the amine compound, such as the elementary processes (ii) to (iv), matches the reaction rate of the elementary process (i) even at room temperature. Proceed at a different speed. However, in general, the reduction reaction involving an amine compound, such as elementary processes (ii) to (iv), proceeds slowly at room temperature. Therefore, under the conditions of the present invention in which the concentration of the amine compound is set low, a liquid reaction is not possible. It is possible to advance the reaction for the first time by heating the temperature to 80 ° C. or higher and stirring. In addition, when the amine compound or fatty acid contained in the liquid phase in which the fatty acid and the amine compound are uniformly mixed has a high vapor pressure at the heating temperature, it should be dissipated from the liquid phase by transpiration due to heating. There is a need to prevent. Similarly, regarding the solvent added to the liquid phase, when it has a high vapor pressure at the heating temperature, it is necessary to prevent the solvent from escaping from the liquid phase due to transpiration due to heating.

  When the silver oxide dispersion mixture is heated and stirred, the heating temperature of the liquid phase under reflux does not exceed the boiling point of the liquid amine compound itself, but at least the fatty acid and the amine compound are uniformly mixed. It is necessary to select a range that exceeds the temperature at which the mixture can form a uniform mixture. Specifically, at room temperature (25 ° C.), when the fatty acid and the amine compound are uniformly mixed to form an addition salt complex, the addition salt complex is dissociated, The form which heat-stirs is employ | adopted to the temperature which exists in the state which liberated the fatty acid and the amine compound. At least the heating temperature of the liquid phase under reflux is 80 ° C. or higher. Usually, the fatty acid is a straight chain alkanoic acid having 14 to 22 carbon atoms or a straight chain alkenoic acid having 14 to 22 carbon atoms, particularly a straight chain alkanoic acid having 14 to 18 carbon atoms, or a straight chain having 14 to 18 carbon atoms. In selecting the chain alkenoic acid, in order to appropriately promote the reaction of reducing the fatty acid silver produced in the elementary process (i) in the presence of the amine compound, at least the heating temperature of the liquid phase under reflux is determined. It is preferable to select the temperature within a range of 80 ° C. or higher and not exceeding the boiling point of the liquid amine compound itself. However, in controlling the temperature at which the reaction rate for producing fatty acid silver from silver (I) is not excessive, the liquid temperature during the heating greatly contributes to the radical reduction reaction due to the decomposition of the fatty acid silver itself. It is preferable to select a range that does not reach the temperature. For example, it is preferable that the temperature does not exceed 140 ° C.

On the other hand, for example, reduction reactions involving amine compounds, such as elementary processes (ii) to (iv), are accelerated at an accelerated rate as the reaction solution temperature increases. However, the overall reaction rate is the reaction rate of the elementary process (i), that is, the rate of formation of fatty acid silver and the rate of the reduction reaction involving the amine compound, such as elementary processes (ii) to (iv), that is, It is determined by the balance with the disappearance rate of fatty acid silver. In the present invention, the fatty acid concentration in the reaction solution, which controls the reaction rate of the elementary process (i): C [R′-COOH] and the reactivity of the fatty acid used: k ₁ are adjusted, and the elementary process (ii). The amine compound concentration in the reaction solution: C [R ¹ R ² R ³ N] and the reactivity of the amine compound used, which controls the rate of the reduction reaction involving the amine compound as in (iv): k ₂ By adjusting the concentration, the concentration of fatty acid silver existing in the reaction system: C [R′-COOAg] is controlled within a desired range.

  That is, one or more fatty acids selected from aliphatic carboxylic acids, in particular, saturated aliphatic monocarboxylic acids or unsaturated aliphatic monocarboxylic acids, per mole of silver atoms contained in the powdered silver oxide (I). , The total of the carboxy groups is 0.02 to 0.05 mol, preferably 0.025 to 0.045 mol, and usually 0.03 to 0.04 mol. The liquid amine compound has a sum of amino nitrogen atoms in the range of 0.12 to 0.35 mol, preferably 0.15 to 0.30 mol, usually 0.2 to 0.3 mol. The amount is an amount.

Based on the reduction reaction process involving an amine compound such as elementary processes (ii) to (iv), the amine compound is reduced when 0.04 mol of silver atoms contained in the powdered silver oxide (I) is reduced. 0.02 molar amount of (R ¹ R ² R ³ N) is consumed. On the other hand, proceeds at higher temperatures, the process (vi) through, by reproducing once consumed amine compound (R ¹ R ² R ³ N), the amine compound in the reaction system (R ¹ R ² R ³ N) A decrease in concentration is avoided. In this process (vi), fatty acid (R ″ —CH ₂ —CH ₂ —COOH) consumes one carbon (CH ₂ ), but is converted to fatty acid (R ″ —CH ₂ —COOH). In practice, a reduction in the sum of the concentrations of fatty acids in the reaction system is also avoided.

Therefore, the liquid amine compound has a sum of amino nitrogen atoms of 0.12 to 0.35 mol, preferably 0.15 to 0.30 mol, usually 0.2 to 0.3 mol. By using the amount, the amine compound concentration in the reaction system: C [R ¹ R ² R ³ N] decreases transiently with the consumption of the amine compound (R ¹ R ² R ³ N). However, since the regeneration is performed through the above-described process, the reduction ratio can be relatively small. In addition, since the amine compound concentration in the reaction system: C [R ¹ R ² R ³ N] is maintained at a certain level or higher, the amine compound used on the surface of the silver fine particles to be generated is Using the lone electron pair present on the amino nitrogen atom, a form formed by coating via a coordination bond is achieved. On the other hand, based on a reduction reaction process involving an amine compound, such as elementary processes (ii) to (iv), the fatty acid used in elementary process (i) is a progression of elementary processes (ii) to (iv). As a result of the regeneration, the sum of the fatty acid concentration in the reaction solution: C [R′-COOH] is also maintained at a substantially constant concentration during the entire reaction.

The reaction of the elementary process (i) is a reaction to the surface of the powdered silver oxide (I), and the surface density of the silver (I) oxide exposed on the surface; C _s [Ag ₂ O] Dependent. Therefore, the temporal change in the concentration of fatty acid silver present in the reaction system: C [R′-COOAg] is approximately expressed as follows.

dC [R'-COOAg] / dt
_{= K 1 × C [R'-} COOH] · C s [Ag 2 O] -k 2 × C [R 1 R 2 R 3 N] · C [R'-COOAg]
Powdered silver oxide (I) itself is a solid, and the surface density of silver oxide (I) exposed on the surface; C _s [Ag ₂ O] does not substantially change. That is, when the reaction form of the present invention is selected, when the reaction temperature is kept constant when the entire reaction proceeds, the fatty acid concentration in the reaction solution: C [R′-COOH] and the reactivity of the fatty acid used. : K ₁ , amine compound concentration in the reaction solution: C [R ¹ R ² R ³ N] and reactivity of amine compound used: k ₂ , exposed on the surface of the dispersed powdered silver oxide (I) Since the surface density of the silver (I) oxide; C _s [Ag ₂ O] is kept substantially constant, as a result, the entire reaction system has an equilibrium condition: dC [R′-COOAg] / dt = It can be regarded as a state satisfying zero. Accordingly, the concentration C [R′-COOAg of the fatty acid silver present in the reaction system while the reaction for forming metallic silver fine particles proceeds using powdered silver oxide (I) dispersed in the reaction solution as a raw material. ] Is also maintained at a substantially constant concentration. Specifically, the concentration C [R′-COOAg] of fatty acid silver present in the reaction system is approximately expressed as follows.
C [R′-COOAg] = (k ₁ × C [R′-COOH] / k ₂ × C [R ¹ R ² R ³ N]) · C _s [Ag ₂ O]
In this case, the amount of silver atoms generated per unit time and unit volume is the amount of fatty acid silver consumed by the reaction per unit time and unit volume: k ₂ × C [R ¹ R ² R ³ N ] · C [R'-COOAg] or the amount of powdered silver oxide (I) consumed in the reaction: k ₁ × C [R'-COOH] · C _s [Ag ₂ O] . In other words, the amount of silver atoms generated per unit time and unit volume is also maintained substantially constant, so that the average particle diameter of the formed metal silver fine particles exhibits high homogeneity. Become.

On the other hand, the reactivity of fatty acid used: k ₁ depends on the type of fatty acid and the reaction liquid temperature, and the reactivity of amine compound used: k ₂ also depends on the kind of amine compound and the reaction liquid temperature. In controlling the average particle diameter of the metallic silver fine particles to be generated within a desired range, the coefficient ratio (k ₁ × C [R′-COOH] / k ₂ × C [R ¹ R ² R ³ N]) It is necessary to adjust the balance to a desired range. The reaction liquid temperature is selected to be high, the reactivity of the fatty acid used: k ₁ , and the reactivity of the amine compound used: k ₂ are taken advantage of, and the amount used is reduced accordingly. A nonpolar solvent for dilution is added to the solution, and the concentration of both in the reaction solution is suppressed to adjust the reaction rate to an appropriate value.

In the present invention, since the reaction temperature is increased, the surface density of silver oxide (I) exposed on the surface of the dispersed powdered silver oxide (I); C _s [Ag ₂ O] is excessively high. As a result, the concentration of fatty acid present in the reaction system: C [R ″ —CH ₂ —CH ₂ —COOH] becomes excessively low. In this case, the regeneration rate of the amine compound through the process (vi) is relatively high. As a result, as a whole, the reduction rate of the powdered silver oxide (I) to form the metal silver fine particles is rather decreased, that is, the dispersed powder form. regard C _s [Ag ₂ O], an appropriate range is present this surface density; the surface density of the silver oxide is exposed on the surface of the silver oxide (I) (I). C s [Ag 2 O ] Represents the content ratio of the powdered silver oxide (I) dispersed in the reaction solution and the powdered silver oxide (I In the present invention, the average particle size of the powdered silver oxide (I) is selected within the range of 200 mesh or less (75 μm or less), and correspondingly, Regarding the content ratio of the powdered silver oxide (I), the silver content ratio in the mixed liquid at the start of the reaction is in the range of 25% by mass to 40% by mass, generally 30% by mass to 40% by mass. It is preferable to select the range.

The nonpolar solvent added to the reaction solution is preferably a nonpolar solvent capable of forming a uniform mixed solution with the liquid amine compound at least at the heating temperature of the liquid phase under reflux. For example, the nonpolar solvent is more preferably selected from toluene, xylene, and a hydrocarbon solvent having a boiling point of 90 ° C. or higher. Since these nonpolar solvents can form a uniform mixed solution through hydrophobic interaction with a hydrocarbon group in a liquid amine compound (R ¹ R ² R ³ N), silver produced When taking a form in which the amine compound is coated on the fine particle surface through a coordinate bond using a lone electron pair present on the amino nitrogen atom, in the nonpolar solvent, Exhibits good dispersibility.

In the present invention, as a more preferable example of the fatty acid used, particularly a linear alkanoic acid having 14 to 18 carbon atoms, myristic acid (tetradecanoic acid, C ₁₃ H ₂₇ COOH; molecular weight 228.38, double melting point) As a more preferable example of linear alkenoic acid having 14 to 18 carbon atoms such as 53.8 ° C. & 57.5 to 58 ° C., boiling point 248.7 ° C. (100 mmHg)), oleic acid ((Z) -9- Octadecenoic acid, C ₁₇ H ₃₃ COOH; molecular weight 282.46, melting point 13.4 ° C., boiling point 286 ° C.). Moreover, when selecting the usage-amount of the fatty acid utilized to a relatively high ratio, the total of the carboxy group is 0.03-per 1 mol amount of silver atoms contained in powdered silver oxide (I), for example. When selecting an amount in the range of 0.05 mol, usually 0.03 to 0.04 mol, a straight chain alkanoic acid having 12 or more carbon atoms such as lauric acid (dodecanoic acid, C ₁₁ H ₂₃ COOH; molecular weight 200.32, melting point 44 ° C., boiling point 225 ° C. (100 mmHg)) can also be suitably used.

When a long-chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH) is used, an amine compound (R ¹ R ² R ³ N) present in an excessive amount in the reaction system, and R ¹ R ² As a result of forming a complex in the form of R ³ N... HOOC— (CH ₂ ) _m —COOH, only one carboxy group can participate in the reaction in the elementary process (i). In consideration of the reactivity of the complex in the form of R ¹ R ² R ³ N... HOOC— (CH ₂ ) _m —COOH, the alkylene chain (— (CH ₂ ) _m —) has a carbon number of 13 or more. If it is, it will become a suitable range of reactivity. The upper limit is more preferably about 18 carbon atoms. Of course, the reactivity of ω-hydroxyalkanoic acid (HO— (CH ₂ ) _m−1 —COOH) produced from long chain dicarboxylic acid (HOOC— (CH ₂ ) _m —COOH) has the corresponding long chain There is no substantial difference from the monocarboxylic acid. Furthermore, a branched alkanoic acid (or a branched alkenoic acid) in which a branched chain is added at a position far from the carboxy group to the alkyl chain of the linear alkanoic acid (or the alkenyl chain of the linear alkenoic acid) described above. ) Is only slightly different from the original linear alkanoic acid (linear alkenoic acid). Therefore, as for the branched alkanoic acid (or branched alkenoic acid), those having the longest unbranched carbon chain portion of about 10 to 17 carbon atoms can also be suitably used.

On the other hand, since the reaction temperature is set high, the reactivity of the fatty acid (R′-COOH) itself used is high, and when the fatty acid concentration in the reaction solution: C [R′-COOH] is high, The following secondary reaction pathway occurs.
(I) Ag ₂ O + R′—COOH → [R′—COOAg + AgOH]
(I ′) [AgOH] + R′—COOH → R′—COOAg + H ₂ O
As a result, when the concentration of fatty acid silver existing in the reaction system: C [R′-COOAg] becomes unnecessarily high, it becomes a factor that impairs controllability of the particle diameter of the silver fine particles to be produced. In order to suppress this secondary reaction route, the addition amount of the fatty acid is selected within an appropriate range, and a nonpolar solvent for dilution is added to the fatty acid concentration in the reaction solution: C [R′-COOH. ] Is preferably reduced to suppress the progress of the secondary reaction.

On the other hand, the liquid amine compound used in the reduction reaction process involving an amine compound is a primary amine (R ¹ NH ₂ ), a secondary amine (R ¹ R ² NH), or a tertiary amine (R ¹ R). ² R ³ N) is preferably selected. Among these, the liquid amine compound includes a primary amine (R ¹ NH ₂ ), a secondary amine (R ¹ R ² NH), and a tertiary amine in which the hydrocarbon group substituted on the amino nitrogen atom is an alkyl group. More preferably, it is an alkylamine selected from any of (R ¹ R ² R ³ N). At that time, when the reaction liquid temperature is 80 ° C. or higher, the liquid amine compound is at least an alkylamine having a boiling point exceeding 100 ° C., more preferably a boiling point exceeding 140 ° C. desirable. Specifically, as an example of a suitably usable alkylamine, as a tertiary amine (R ¹ R ² R ³ N), tributylamine (molecular weight: 185.36, boiling point: 213.5 ° C.), trihexylamine ( The secondary amine (R ¹ R ² NH) such as molecular weight 269.51 and boiling point 264 ° C., dimethyloctylamine (molecular weight 157.3, boiling point 195 ° C.) and the like are dibutylamine (molecular weight 129.25, boiling point 159 ° C. ( 761 mmHg)), di-2-ethylhexylamine (molecular weight 241.46, boiling point 123 ° C./5 mmHg), and the like as primary amine (R ¹ NH ₂ ), dodecylamine (molecular weight 185.35, melting point 28.3 ° C., Boiling point 247 ° C. to 249 ° C.), 2-ethylhexylamine (molecular weight 129.24, boiling point 169 ° C.) and the like.

In addition, the amine oxide type compound [R ¹ R ² R ³ N ⁺ —O ⁻ or R ¹ R ² R ³ N → O] as an intermediate product is derived from, for example, a secondary amine (R ¹ R ² NH). The amine oxide type compound [R ¹ R ² HN → O] and the amine oxide type compound [R ¹ H ₂ N → O] derived from the primary amine (R ¹ NH ₂ ) have a high reaction temperature and a hydroxyamine. A transfer reaction to [R ¹ R ² N—OH, R ¹ HN—OH] easily occurs. Considering this point, when selecting a relatively high reaction temperature, use a tertiary amine (R ¹ R ² R ³ N), particularly a trialkylamine having a boiling point exceeding 140 ° C. Is more preferable.

Furthermore, two silver atoms are produced from silver oxide (I) (Ag ₂ O) through an elementary reaction process that can be promoted due to the amine effect as described above. When undergoing oxidation to an oxide type compound [R ¹ R ² R ³ N ⁺ —O ⁻ or R ¹ R ² R ³ N → O], as a reaction intermediate, a cation radical species [R ¹ R ² R ³ N ⁺ ·] Is generated. In the process of exhibiting this kind of amine effect, it is necessary that the complex type intermediate formation of [R′-COOAg... NR ¹ R ² R ³ ] proceeds easily. From that viewpoint, tertiary amine (R ¹ R ² R ³ N), in which the hydrocarbon group substituted on the nitrogen atom is an alkyl group, is more preferable. In addition, from the amine oxide type compound [R ¹ R ² R ³ N ⁺ —O ⁻ or R ¹ R ² R ³ N → O], in the molecule, by rearrangement of a hydrogen atom on the alkyl group β carbon, an alkene ( R—CH═CH ₂ ) and hydroxyamine [R ¹ R ² N—OH] may proceed to disproportionation decomposition. Considering this reaction as well, a tertiary amine (R ¹ R ² R) in which the hydrocarbon group substituted on the nitrogen atom is at least an alkyl group having 2 or more carbon atoms, preferably an alkyl group having 3 or more carbon atoms. ³ N) is more preferred.

In the present invention, the above process (vi) is used. Since this process (vi) is a reaction involving decarboxylation, it does not proceed when the reaction temperature is low. By setting it as the above, the reaction rate is increasing. As a result of the above process (vi) being repeated, the carbon chain of the linear alkanoic acid is finally reduced. Propanoic acid (CH ₃ CH ₂ COOH; boiling point 140.8 ° C.) or butanoic acid (CH ₃ CH ₂ CH ₂ COOH; boiling point 164.05 ° C.). The liquid temperature during the reaction is selected in the range of 80 ° C. to 140 ° C., and usually a reflux condenser is used for the purpose of preventing the solvent from evaporating out of the reaction system. The evaporation of small linear alkanoic acids out of the system is also avoided.

  In the liquid phase of the reaction system, the fatty acid and the liquid amine compound are present in a state of being uniformly dissolved in the solvent. In the liquid phase of this reaction system, the boiling point rises due to these solutes dissolved in the solvent, and the boiling point of the solvent in this mixed solution is slightly higher than the boiling point of the solvent alone. It is temperature. In general, when a mixed solution is heated, a reflux condenser is used for the purpose of preventing evaporation of the solvent of the mixed solution, but the liquid temperature cannot be made higher than the reflux temperature of the solvent used. In other words, it is necessary to select the type of the solvent to be used based on the boiling point so that the reflux temperature of the solvent to be used is higher than the liquid temperature at the target reaction.

  For example, toluene (boiling point 110.6 ° C.) can be suitably used in a system where the liquid temperature during the reaction is 110 ° C. or less. Xylene (p-xylene; boiling point 138.3 ° C.) can be suitably used in a system in which the liquid temperature during the reaction is 140 ° C. or lower in consideration of an increase in boiling point. In addition, a hydrocarbon solvent having a boiling point of 90 ° C. or higher can be used as the solvent, and in this case, the hydrocarbon solvent can be suitably used. The liquid temperature during the reaction is within the range of the boiling point or less of the hydrocarbon solvent itself. is there.

  In addition, although the boiling point of the fatty acid utilized generally exceeds 140 degreeC, the boiling point of the liquid amine compound to be used may be in the range of 140 degrees C or less depending on the kind. Usually, the boiling point of the liquid amine compound used is higher than the boiling point of the solvent used, but depending on the type, the boiling point of the liquid amine compound may be lower than the boiling point of the solvent used. Also occurs very rarely. In this rare case, since the boiling point of the liquid amine compound is lower than the boiling point of the solvent used, it is necessary to prevent evaporation of the dissolved liquid amine compound using a reflux condenser. . On the other hand, since a reflux condenser is used, the liquid amine compound is refluxed between the liquid phase and the gas phase of the reaction system, and the liquid temperature of the mixed liquid is the reflux temperature of the liquid amine compound. It cannot be raised above the temperature. For example, when a mixture of a plurality of types of amine compounds is used in combination as a liquid amine compound, if one of the amine compounds used accidentally has a lower boiling point than the solvent, the amine that exhibits this lower boiling point is used. The temperature of the mixed solution cannot be increased above the reflux state of the compound between the liquid phase and the gas phase of the reaction system, that is, the reflux temperature.

  In other words, in the present invention, the heating temperature of the liquid phase is at least 80 ° C. or more, and the temperature at which the mixture formed by uniformly mixing the fatty acid and the amine compound can form a uniform mixed solution. And a temperature range that does not exceed the boiling point of the liquid amine compound itself. When the boiling point of the liquid amine compound itself is 100 ° C. or higher, the heating temperature of the liquid phase is at least 100 ° C. or higher, and the temperature is selected so as not to exceed the boiling point of the liquid amine compound itself. It will be.

  Therefore, in the present invention, in order to arbitrarily select the heating temperature of the liquid phase in the range of 80 ° C. to 140 ° C., at least the boiling point of the solvent used and the boiling point of the liquid amine compound used are It is generally necessary that the temperature be higher than the heating temperature of the selected liquid phase. Furthermore, in order to arbitrarily select the heating temperature of the liquid phase in the range of 80 ° C to 140 ° C, it is desirable that at least the boiling point of the liquid amine compound to be used is 140 ° C or higher.

In the present invention, in the process of producing silver nanoparticles from the dispersed powdered silver oxide (I), the oxygen atoms constituting the silver oxide (I) are not water molecules (H ₂ O). The carbon dioxide (CO ₂ ) is removed from the reaction system. Furthermore, when a reflux condenser is used, water molecules (H ₂ O) are produced as by-products in the elementary process (vi), but free water molecules (H ₂ O) accumulate in the reaction system. Therefore, the heating temperature of the liquid phase during the reaction can be set to a temperature exceeding 100 ° C.

In the present invention, powdered silver oxide (I) is used as a raw material, and metal silver fine particles are formed through a reduction reaction in the liquid phase. The formed metal silver fine particles are in contact with each other to form a plurality of fine particles. In order to avoid the phenomenon that the agglomerates are fused, the surface of the generated metal silver fine particles is densely covered with organic molecules present in the reaction system. At that time, since an excessive amount of amine compound is present in the reaction system, at least the amine compound; [R ¹ R ² R ³ N] is present on the amino nitrogen with respect to the surface of the silver fine particles to be generated. It is possible to take a form in which a lone electron pair existing on an atom is used to coat through a coordination bond.

  In the reaction system, fatty acid silver [R′-COOAg] often undergoes a reduction reaction using an amine compound after being adsorbed on the surface of the silver fine particles to be produced. At that time, when the reduction reaction is completed, the fatty acid (R′-COOH) is liberated, but in part, the fatty acid (R′-COOH) remains on the surface of the metal silver fine particles as a ligand. It is also possible to indicate the existing form.

Usually, at least the amine compound; [R ¹ R ² R ³ N] is coordinated to the surface of the silver fine particles to be generated by utilizing a lone electron pair existing on the amino nitrogen atom. In the stage of taking a form formed by coating with a plurality of [R ¹ R ² R ³ N], there is more difference between the boiling point and the liquid temperature during the reaction. Larger ones make a greater contribution to the formation of the coating layer. In other words, in a reduction reaction process involving an amine compound such as the elementary processes (ii) to (iv) described above, a tertiary amine (R ¹ R ² R ³ N) having a high boiling point is used. It is a more preferable form, and at the same time, it is also suitable for use in forming a coating layer.

  In the present invention, the total amount of the amine compound added is reduced, and the amine compound used in the reduction reaction process involving the amine compound, such as the elementary processes (ii) to (iv) described above, is produced. The same amine compound is used as the amine compound used in the process of forming the coating layer on the surface of the silver fine particles.

  In addition, stirring and heating under reflux are carried out while passing an inert gas through the reaction system so that the generated silver atoms are not re-oxidized by oxygen molecules dissolved in the reaction mixture, and then into the reaction mixture. It is preferable to prevent dissolution of oxygen molecules. In addition, since the liquid amine compound or the nonpolar solvent itself used for dilution has poor oxygen molecule solubility, the oxygen concentration dissolved in the reaction solution is originally low. In addition, when heating and refluxing, oxygen molecules dissolved in the reaction mixture are evaporated, and as a result, the possibility that oxygen molecules are mixed into the reaction mixture is extremely low. Therefore, it is not always necessary to vent the inert gas and replace the reaction system with the inert gas so that fresh air does not enter the reaction system from the outside. In addition, when stirring and heating reflux are performed while venting an inert gas through the reaction system, it is preferable to use one or more types selected from the group consisting of nitrogen, argon, and helium as the inert gas. In addition, when stirring and heating reflux are performed while ventilating the inert gas, it is necessary to prevent the fatty acid, the amine compound, and the nonpolar solvent from evaporating along with the aerated inert gas.

  In addition, after a series of reactions are completed, after the liquid temperature is lowered, as an operation to separate the metallic silver fine particles dispersed in the reaction mixture from the remaining amine compound and fatty acid, an amine compound, A polar solvent capable of dissolving a fatty acid is added, and metallic silver fine particles having a coating molecular layer that exposes a hydrophobic hydrocarbon group on the surface are allowed to settle to separate the liquid phase. Specifically, when a polar solvent having a low boiling point and an alcohol having 3 or less carbon atoms, for example, methanol, alkyl ketones such as acetone, are added to the reaction mixture, the remaining amine compound and fatty acid are reduced to this low level. Dissolves in boiling polar solvent. On the other hand, the metal silver fine particles having a coating molecular layer that expresses a hydrophobic hydrocarbon group on the surface cannot precipitate sufficient dispersion characteristics in such a low boiling polar solvent, and thus settle. The precipitated metallic silver fine particles having a covering molecular layer are recovered by solid-liquid separation. A slightly residual polar solvent is evaporated and redispersed again in a non-polar solvent to obtain a dispersion of metallic silver fine particles having a target average particle size in the range of 3 nm to 20 nm, more preferably in the range of 4 nm to 15 nm. Can be prepared.

  As described above, in the reaction mixture, one or more fatty acids per one mole amount of silver atoms contained in the fine powdered silver oxide (I) as a raw material, the total of carboxy groups is 0.02 to 0. 0.05 mol amount, preferably 0.025 to 0.045 mol amount, usually 0.03 to 0.04 mol amount in a range of 0.03 to 0.04 mol amount and a liquid amine compound, the total of amino nitrogen atoms is 0 .12 to 0.35 mole amount, preferably 0.15 to 0.30 mole amount, usually in an amount ranging from 0.2 to 0.3 mole amount. In order to maintain the dispersion state of the generated metallic silver fine particles, a diluting solvent is used to optimize the volume of the reaction solution. However, since the total amount of fatty acid and liquid amine compound used is not large, the content ratio of the raw material fine powdery silver oxide (I) contained in the reaction mixture is relatively high. In other words, a reduction reaction to a relatively large amount of finely powdered silver (I) oxide is possible using a reaction vessel having a certain capacity, which is a method suitable for mass production of metal silver fine particles. .

  The reaction time is appropriately selected depending on the amount ratio of the fatty acid used, the type of fatty acid used, and the reaction solution temperature per mole of silver atoms contained in the fine powdery silver oxide (I) as a raw material. It is what is done. At this time, when the particle size of the raw fine powdery silver oxide (I) is increased, the time required for disappearance of the raw fine powdery silver oxide (I) by the reaction with the fatty acid occurring on the surface thereof becomes longer. Therefore, it is preferable to reduce the particle size and to uniformly disperse the reaction solution in the solution while heating and stirring. In particular, it is more preferable to use a particle size distribution that falls within a range of 200 mesh or less (75 μm or less).

  In the present invention, metallic silver fine particles are formed from fine powdered silver oxide (I) as a raw material, and the reduction reaction process is not to reduce the amine (after reducing the total amount of silver (I) oxide to fatty acid silver). By adopting a method of reducing fatty acid silver in the presence of an amine compound while gradually producing fatty acid silver from silver (I) oxide, a nano-scale fine particle size showing a highly uniform particle size distribution Silver fine particles having

  The rate at which fatty acid silver is produced from finely powdered silver oxide and then the rate at which silver atoms are produced by reduction are determined by the type and amount of fatty acid (concentration in the reaction solution) and the amine compound used in the reduction reaction. By properly controlling and adjusting the type, amount added (concentration in the reaction solution), and liquid temperature within the above range, it can be controlled within a balanced range. As a result, metallic silver fine particles with a desired particle size can be obtained. Can be obtained with high reproducibility.

  Hereinafter, the present invention will be described more specifically by showing specific examples. Although these specific examples are examples of the best mode according to the present invention, the present invention is not limited by these specific examples.

(Example 1)
In a 100 mL round bottom flask, powdered silver (I) oxide (Ag ₂ O: molecular weight 231.74,
Purity 99%) 30 mmol, oleic acid ((Z) -9-octadecenoic acid, C ₁₇ H ₃₃ COOH; molecular weight 282.46, melting point 13.4 ° C., boiling point 286 ° C.) 1.8 mmol, tributylamine (molecular weight 185.36) 8.4 mmole, boiling point 213.5 ° C., purity 99%), and toluene (boiling point 110.6 ° C.) is added as a solvent to adjust the content of silver contained in the liquid to 35% by mass. While stirring this reaction liquid, the liquid temperature is raised to 110 ° C. over about 40 minutes. During heating and reaction, a reflux condenser is used to prevent evaporation of the solvent toluene.

In this temperature rising process, when the liquid temperature exceeded 70 ° C., the reaction liquid gradually began to exhibit a dark brown color. After the temperature rise, the liquid temperature is kept at 110 ° C. and stirring is continued for 10 minutes. During that time, all of the silver (I) oxide powder disappeared, and the reaction solution became a uniform liquid with a dark brown color. Heating was stopped, and the reaction solution was cooled to room temperature (20 ° C.) while stirring. The time from when the liquid temperature exceeded 70 ° C. until the heating was stopped was about 25 minutes (15 minutes + 10 minutes).

  Thereafter, the dark brown liquid was transferred to a beaker, and 200 g of methanol was added to coagulate and precipitate the hydrophobic colloid. Next, the supernatant (methanol solution) was removed by suction by decantation and dried at 80 ° C. to recover the powder. When the metal component contained in the dried powder was subjected to powder X-ray diffraction, it was confirmed to be fcc structured metal silver. The silver content in the powder was calculated as 85% by mass from thermal analysis. The dispersion solution obtained by redispersing this powder in toluene exhibited plasmon absorption peculiar to silver nanoparticles at 380 to 450 nm. It was also confirmed that a uniform coating layer was formed on the surface of the silver nanoparticles by the organic molecular species. This coating layer of organic molecular species fulfills the function of imparting dispersibility in the nonpolar solvent toluene. It was also confirmed that the coating layer of organic molecular species on the surface of the silver nanoparticles contained at least tributylamine.

  In addition, as a result of evaluating the average particle diameter of the produced | generated silver nanoparticle, the average particle diameter of the silver nanoparticle which has a coating layer by the said organic molecular species was 7 nm.

Moreover, the silver finally recovered as silver nanoparticles was 98% with respect to the silver contained in the powdery silver oxide (I) as a raw material.

(Example 1-1)
In this example, the heating rate was changed with respect to the reaction conditions of Example 1,
In a 100 mL round bottom flask, powdered silver (I) oxide (Ag ₂ O: molecular weight 231.74,
Purity 99%) 30 mmol, oleic acid ((Z) -9-octadecenoic acid, C ₁₇ H ₃₃ COOH; molecular weight 282.46, melting point 13.4 ° C., boiling point 286 ° C.) 1.8 mmol, tributylamine (molecular weight 185.36) 8.4 mmole, boiling point 213.5 ° C., purity 99%), and toluene (boiling point 110.6 ° C.) is added as a solvent to adjust the content of silver contained in the liquid to 35% by mass. While stirring this reaction solution, the solution temperature is increased to 110 ° C. over about 20 minutes. During heating and reaction, a reflux condenser is used to prevent evaporation of the solvent toluene.

In this temperature rising process, when the liquid temperature exceeded 70 ° C., the reaction liquid gradually began to exhibit a dark brown color. After the temperature rise, the liquid temperature is kept at 110 ° C. and stirring is continued for 10 minutes. During that time, all of the silver (I) oxide powder disappeared, and the reaction solution became a uniform liquid with a dark brown color. Heating was stopped, and the reaction solution was cooled to room temperature (20 ° C.) while stirring. The time from when the liquid temperature exceeded 70 ° C. until the heating was stopped was about 15 minutes (5 minutes + 10 minutes).

Thereafter, the dark brown liquid was transferred to a beaker, and 200 g of methanol was added to coagulate and precipitate the hydrophobic colloid. Next, the supernatant (methanol solution) was removed by suction by decantation. Next, 50 mL of heptane (boiling point 98.4 ° C.) was added to the coagulating and precipitated hydrophobic colloid to redisperse and stirred while heating to 80 ° C. to evaporate residual methanol. After cooling, in order to remove solid components having a large particle size such as unreacted powdered silver oxide (I), the obtained dispersion solution was filtered through a 0.2 μm membrane filter, and the dispersion solution was recovered. This dispersion solution showed plasmon absorption peculiar to silver nanoparticles at 380 to 450 nm. It was also confirmed that a uniform coating layer was formed on the surface of the silver nanoparticles by the organic molecular species. This coating layer of organic molecular species fulfills the function of imparting dispersibility in the nonpolar solvents toluene and heptane. It was also confirmed that the coating layer of organic molecular species on the surface of the silver nanoparticles contained at least tributylamine.

  In addition, as a result of evaluating the average particle diameter of the produced | generated silver nanoparticle, the average particle diameter of the silver nanoparticle which has a coating layer by the said organic molecular species was 7 nm.

Moreover, the silver finally recovered as silver nanoparticles was 90% with respect to the silver contained in the raw material powdered silver oxide (I).

  In Example 1-1, compared to Example 1, the total time of heating to 70 ° C. or more is shorter. The difference in the recovery yield of the silver nanoparticles is caused by the difference in the total heating time.

(Example 2)
In this example, in place of oleic acid used in the reaction conditions of Example 1, myristic acid (tetradecanoic acid, C ₁₃ H ₂₇ COOH; molecular weight 228.38, double melting point 53.8 ° C. & 57.5-58 The reaction was carried out under the same conditions except that the temperature was 0 ° C. and the boiling point was 248.7 ° C. (100 mmHg). During heating and reaction, a reflux condenser is used to prevent evaporation of the solvent toluene.

Similarly, in the temperature rising process, when the liquid temperature exceeded 70 ° C., the reaction liquid gradually began to exhibit a dark brown color. After the temperature rise, the liquid temperature is kept at 110 ° C. and stirring is continued for 10 minutes. In the meantime, the silver (I) oxide powder disappeared, and the reaction solution became a uniform liquid with a dark brown color. Heating was stopped, and the reaction solution was cooled to room temperature (20 ° C.) while stirring. The time from when the liquid temperature exceeded 70 ° C. until the heating was stopped was about 25 minutes (15 minutes + 10 minutes).

Thereafter, the obtained dark brown liquid was transferred to a beaker, and 200 g of methanol was added to coagulate and precipitate the hydrophobic colloid. Next, the supernatant (methanol solution) was removed by suction by decantation. Next, 50 mL of heptane (boiling point 98.4 ° C.) was added to the coagulating and precipitated hydrophobic colloid to redisperse and stirred while heating to 80 ° C. to evaporate residual methanol. After cooling, in order to remove solid components having a large particle size such as unreacted powdered silver oxide (I), the obtained dispersion solution was filtered through a 0.2 μm membrane filter, and the dispersion solution was recovered. This dispersion solution showed plasmon absorption peculiar to silver nanoparticles at 380 to 450 nm. It was also confirmed that a uniform coating layer was formed on the surface of the silver nanoparticles by the organic molecular species. This coating layer of organic molecular species fulfills the function of imparting dispersibility in the nonpolar solvents toluene and heptane. It was also confirmed that the coating layer of organic molecular species on the surface of the silver nanoparticles contained at least tributylamine.

  In addition, as a result of evaluating the average particle diameter of the produced | generated silver nanoparticle, the average particle diameter of the silver nanoparticle which has a coating layer by the said organic molecular species was 12 nm.

Further, finally recovered silver as silver nanoparticles was 92% with respect to silver contained in the raw material powdered silver oxide (I).

(Example 3)
In this example, trihexylamine (molecular weight 269.51 and boiling point 264 ° C.) was used instead of tributylamine used in the reaction conditions of Example 1, and the other conditions were selected and reacted. Went. During heating and reaction, a reflux condenser is used to prevent evaporation of the solvent toluene.

Similarly, in the temperature rising process, when the liquid temperature exceeded 70 ° C., the reaction liquid gradually began to exhibit a dark brown color. After the temperature rise, the liquid temperature is kept at 110 ° C. and stirring is continued for 10 minutes. In the meantime, the silver (I) oxide powder disappeared, and the reaction solution became a uniform liquid with a dark brown color. Heating was stopped, and the reaction solution was cooled to room temperature (20 ° C.) while stirring. The time from when the liquid temperature exceeded 70 ° C. until the heating was stopped was about 25 minutes (15 minutes + 10 minutes).

  Thereafter, the obtained dark brown liquid was transferred to a beaker, and 200 g of methanol was added to coagulate and precipitate the hydrophobic colloid. Next, the supernatant (methanol solution) was removed by suction by decantation. Next, 50 ml of heptane (boiling point 98.4 ° C.) was added to the coagulated and precipitated hydrophobic colloid, and the mixture was redispersed and stirred while heating to 80 ° C. to evaporate residual methanol. After allowing to cool, the obtained dispersion solution was filtered through a 0.2 μm membrane filter, and the dispersion solution was recovered. This dispersion solution showed plasmon absorption peculiar to silver nanoparticles at 380 to 450 nm. It was also confirmed that a uniform coating layer was formed on the surface of the silver nanoparticles by the organic molecular species. This coating layer of organic molecular species fulfills the function of imparting dispersibility in the nonpolar solvents toluene and heptane. It was also confirmed that the coating layer of organic molecular species on the surface of the silver nanoparticles contained at least tributylamine.

  In addition, as a result of evaluating the average particle diameter of the produced | generated silver nanoparticle, the average particle diameter of the silver nanoparticle which has a coating layer by the said organic molecular species was 9 nm.

Moreover, the silver finally recovered as silver nanoparticles was 97% with respect to the silver contained in the powdery silver oxide (I) as a raw material.

Example 4
In this example, dodecylamine (molecular weight: 185.35, boiling point: 247 ° C. to 249 ° C.) was used instead of tributylamine used in the reaction conditions of Example 1, and the same conditions were selected except for that. The reaction was performed. During heating and reaction, a reflux condenser is used to prevent evaporation of the solvent toluene.

In the temperature rising process, when the liquid temperature exceeded 80 ° C., the reaction liquid gradually began to exhibit a dark brown color. After the temperature rise, the liquid temperature is kept at 110 ° C. and stirring is continued for 20 minutes. Meanwhile, silver oxide (I)
Disappeared and the reaction solution became a uniform liquid with dark brown color. Heating was stopped, and the reaction solution was cooled to room temperature (20 ° C.) while stirring. The time from when the liquid temperature exceeded 80 ° C. until the heating was stopped was about 35 minutes (15 minutes + 20 minutes).

Thereafter, the obtained dark brown liquid was transferred to a beaker, and 200 g of methanol was added to coagulate and precipitate the hydrophobic colloid. Next, the supernatant (methanol solution) was removed by suction by decantation. Next, 50 ml of heptane (boiling point 98.4 ° C.) was added to the coagulated and precipitated hydrophobic colloid, and the mixture was redispersed and stirred while heating to 80 ° C. to evaporate residual methanol. After cooling, in order to remove solid components having a large particle size such as unreacted powdered silver oxide (I), the obtained dispersion solution was filtered through a 0.2 μm membrane filter, and the dispersion solution was recovered. This dispersion solution showed plasmon absorption peculiar to silver nanoparticles at 380 to 450 nm. It was also confirmed that a uniform coating layer was formed on the surface of the silver nanoparticles by the organic molecular species. This coating layer of organic molecular species fulfills the function of imparting dispersibility in the nonpolar solvents toluene and heptane. It was also confirmed that the coating layer of organic molecular species on the surface of the silver nanoparticles contained at least tributylamine.

  In addition, as a result of evaluating the average particle diameter of the produced | generated silver nanoparticle, the average particle diameter of the silver nanoparticle which has a coating layer by the said organic molecular species was 13 nm.

Moreover, the silver finally recovered as silver nanoparticles was 89% with respect to the silver contained in the powdery silver oxide (I) as a raw material.

(Example 5)
In this example, the reaction was carried out using xylene (p-xylene; boiling point 138.3 ° C.) as a solvent in place of toluene used in Example 1. During heating and reaction, a reflux condenser is used to prevent evaporation of the solvent xylene.

Similarly, in the temperature rising process, when the liquid temperature exceeded 70 ° C., the reaction liquid gradually began to exhibit a dark brown color. After the temperature rise, the liquid temperature is kept at 125 ° C. and stirring is continued for 5 minutes. In the meantime, the silver (I) oxide powder disappeared, and the reaction solution became a uniform liquid with a dark brown color. Stop heating,
The reaction solution was cooled to room temperature (20 ° C.) while stirring. The time from when the liquid temperature exceeded 70 ° C. until the heating was stopped was about 25 minutes (20 minutes + 5 minutes).

  Thereafter, the obtained dark brown liquid was transferred to a beaker, and 200 g of methanol was added to coagulate and precipitate the hydrophobic colloid.

  Next, the supernatant (methanol solution) was removed by suction by decantation. Next, 50 ml of heptane (boiling point 98.4 ° C.) was added to the coagulated and precipitated hydrophobic colloid, and the mixture was redispersed and stirred while heating to 80 ° C. to evaporate residual methanol. After allowing to cool, the obtained dispersion solution was filtered through a 0.2 μm membrane filter, and the dispersion solution was recovered. This dispersion solution showed plasmon absorption peculiar to silver nanoparticles at 380 to 450 nm. It was also confirmed that a uniform coating layer was formed on the surface of the silver nanoparticles by the organic molecular species. This coating layer of organic molecular species fulfills the function of imparting dispersibility in the nonpolar solvents toluene and heptane. It was also confirmed that the coating layer of organic molecular species on the surface of the silver nanoparticles contained at least tributylamine.

  In addition, as a result of evaluating the average particle diameter of the produced | generated silver nanoparticle, the average particle diameter of the silver nanoparticle which has a coating layer by the said organic molecular species was 10 nm.

Moreover, the silver finally recovered as silver nanoparticles was 98% with respect to the silver contained in the powdery silver oxide (I) as a raw material.

  The present invention is economical, for example, by using inexpensive silver oxide as a raw material for fine metal silver particles that can be used as metal filler fine particles in various fields such as conductive metal pastes and catalysts. We provide manufacturing technology. That is, compared with fine silver fine particles having an average particle diameter of nanometer scale, which has been conventionally produced by applying a gas evaporation method (gas phase method), The liquid phase method using silver oxide as a raw material enables commercial scale mass production.

Claims (9)

A method of preparing metal silver fine particles having an average particle diameter of 3 nm to 20 nm by a reduction reaction in a liquid phase using silver oxide as a raw material,
Per mole of silver atoms contained in the powdered silver oxide (I),
One or more fatty acids selected from saturated aliphatic carboxylic acids or unsaturated aliphatic carboxylic acids, in an amount such that the sum of the carboxy groups is 0.02 to 0.05 mol,
A liquid amine compound is added in an amount such that the sum of amino nitrogen atoms is 0.12 to 0.35 mol,
A nonpolar solvent is added, and the silver content in the mixed solution is selected in the range of 25% by mass to 40% by mass,
Preparing a silver oxide dispersion mixture in which the powdered silver oxide (I) is dispersed in a mixture in which the fatty acid and the amine compound are uniformly mixed;
The silver oxide dispersion mixture is heated and stirred at a liquid temperature selected in the range of 80 ° C. to 140 ° C., and the amino compound is in a liquid phase comprising a mixture in which the fatty acid and the amine compound are uniformly mixed. In the presence of water, the fatty acid is allowed to act on the silver oxide (I) to form the corresponding fatty acid silver (I), and thereafter, metal silver fine particles having an average particle diameter of 3 nm to 20 nm consisting of silver atoms generated by reduction are precipitated. And
The metal silver fine particles having an average particle diameter of 3 nm to 20 nm to be deposited are coordinated with respect to silver atoms on the surface using at least the lone electron pair in which the amine compound is present on the amino nitrogen atom. A method for producing fine metal silver particles, characterized in that the metal silver fine particles are coated through various bonds. The method according to claim 1, wherein the fatty acid is selected from linear alkanoic acids having 14 to 22 carbon atoms or linear alkenoic acids having 14 to 22 carbon atoms. The liquid amine compound includes a primary amine (R ¹ NH ₂ ), a secondary amine (R ¹ R ² NH), and a tertiary amine (R ¹ R ² R ³ N) having a boiling point of 80 ° C. or higher. The production method according to claim 1, wherein the production method is one kind of amine selected from the group or two or more kinds of amines. The liquid amine compound includes a primary amine (R ¹ NH ₂ ), a secondary amine (R ¹ R ² NH), and a tertiary amine (R ¹ ), wherein the hydrocarbon group substituted on the amino nitrogen atom is an alkyl group. The production method according to claim 3, wherein the production method is one kind of amine selected from the group consisting of R ² R ³ N), or two or more kinds of amines. The production method according to claim 4, wherein the liquid amine compound is a trialkylamine having a boiling point exceeding 140 ° C. In the heating and stirring of the silver oxide dispersion mixture, the heating temperature of the liquid phase is at least 80 ° C. or more, and the temperature at which the mixture of the fatty acid and the amine compound is uniformly mixed can form a uniform mixed solution. The method according to claim 1, wherein the temperature is selected so as to exceed the boiling point of the liquid amine compound itself. The heating temperature of the silver oxide dispersion mixture is selected so that the heating temperature of the liquid phase is at least 100 ° C or higher and does not exceed the boiling point of the liquid amine compound itself. 2. The production method according to 1. The method according to claim 1, wherein the nonpolar solvent is a nonpolar solvent capable of forming a uniform mixed solution with the liquid amine compound at a liquid phase heating temperature. The production method according to claim 8, wherein the nonpolar solvent is selected from toluene, xylene, and a hydrocarbon solvent having a boiling point of 90 ° C. or higher.